1. Field of the Invention
The factors defining the aerodynamic characteristics of an aircraft is on one hand the geometry of the supporting surfaces and on the other hand the surface smoothness of the supporting surfaces. Rough surfaces may deteriorate the flying performance to a considerable degree. Ice and snow coatings may cause so rough surfaces that flying is rendered impossible. During flight the built-in de-icing system of the aircraft is sufficient but at ground intervals de-icing must be performed before start under unfavourable meteorological conditions.
2. Description of the Prior Art
In certain cases it might be sufficient to sweep the wings clear of loose snow but more efficient actions are most often required. In general a hot mixture of water and glycol is sprayed, whereby the glycol provides a certain preventive effect, which is intended to remain, until the aircraft has climbed into the air. Upon heavy snow fall the treatment must be performed immediately before start.
The spraying of the de-icing liquid is generally performed by a team consisting of a spraying machine operator and a driver, who drives the tank truck with the spraying machine. The spraying machine operator stands on a lifting platform, from which he treats those portions of the aircraft which can be reached by the jet from the spraying machine. The truck is driven around the aircraft so that all portions of the aircraft can be treated.
Under favourable conditions the aircraft is occupied for only about five minutes by the treatment but time studies have shown that on the average a team will work 45 minutes on each aircraft. It is not rare that delays of air services occur because many planes are queueing to be de-iced. Thus, de-icing will frequently cause a bottle-neck in the traffic capacity of the air port.
The method has been criticized, since excess glycol may penetrate into the ground and in the long run ruin the ground water.
In order to reduce these risks special locations have been arranged at the new air ports of Paris and Montreal, where de-icing is to be performed. Through drainage systems the treatment liquid can be recovered and re-used. De-icing is performed by the aircraft by its own engines passing between two large scaffolds, on which 4 to 6 men are placed. By means of hand-operated jet nozzles the men spray the aircraft as it passes.
In Sweden the authorities have developed an interest in the health risks of the method for the staff involved. Stricter safety directives have been issued.
In U.S. Pat. No. 3,612,075 a central de-icing installation is disclosed consisting of a pair of in the longitudinal direction of the aircraft self-propelled towers on either side of the air-craft. Each tower is provided with a hinged boom, which extends inwardly over the aircraft. By means of a plurality of hinges the boom is pivotable in the vertical plane. The boom carries a conduit with nozzles for spraying de-icing liquid or compressed air. The installation is intended to operate so that the towers are driven in pairs externally of the wing tips along the parked aircraft. The inwardly projecting booms and their hinges are actuated so that the nozzles of the conduit are located adjacent and directed towards the surfaces to be de-iced. The purpose appears to have been to solve the problem of rapidly spraying the necessary surfaces of the aircraft.
The German Offenlegunsschrift No. 2,343,389 discloses an installation for recovering and re-using de-icing liquid and arrangements for spraying de-icing liquid.
In a system of ducts on the parking ramp the de-icing liquid run off from the aircraft, is then collected and conducted in pipes to a purification plant. After having been analyzed with respect to dilution the liquid can either be rejected (should the glycol content be too low) or else be treated by freezing or distillation so that the concentration of glycol is increased. If required, fresh glycol is added to the solution, which is finally heated and stored in a storage tank, until it is to be used again. The inventor of this system appears to presume that a de-icing liquid should be used consisting of a solution of approximately equal parts of water and glycol.
For the spraying of the de-icing liquid it is indicated that two or four vehicles should be placed at strategic locations on the de-icing ramp. Each vehicle is provided with a two-part boom, which is moved inwardly towards the parked aircraft. The boom carries a conduit with a nozzle, through which the liquid is sprayed onto the aircraft.